Electrical motor and generators must often be rebuilt in a manner which includes the replacement of their windings. The new windings are constructed by first winding several turns of insulated conductor, one on top of the other, into a simple, flat coil in the approximate shape of a race track.
The coil is then mounted in a coil spreader, typically being initially held in the vertical plane. Each extreme end of the preformed flat coil is held in position by a knuckle. Relatively nearer each end, but spaced from each knuckle are a pair of clamping jaws, one positioned on vertically opposite sides of the knuckle, typically, an upper knuckle and a lower knuckle, so that the coil is supported by the two knuckles and four such clamps.
In the forming operation the opposed clamps near each end are driven and spread apart from each other and may also be pivoted. Simultaneously, the clamps ordinarily pull the portion of the coil, which is between the knuckle and each clamp, down upon a forming surface to bend that portion into the desired end turn contour so that it will fit properly onto the stator or rotor.
Often the spreading clamps are not spaced equidistantly from their nearby knuckle. Because the clamps must be spread apart to a selected spacing distance which is dependent upon the dimension of the machine upon which the coil is to be installed, the knuckle is typically mounted on an arm which pivots about an axis parallel to the length of the coil so that the knuckle may move freely laterally and no force will be applied by the knuckle on the end turn coil segments between the knuckle and either clamp. This means that the final position of the knuckle with respect to the forming surface and the clamps is undetermined until after the coil has been spread. That fact has presented no problems with prior art spreaders which utilize large, bulky and expensive custom made forming surfaces.
However, in a machine using a universal bending form of the type shown in U.S. Pat. No. 4,450,708, the forming surface, though universal and inexpensively and quickly adjustable to a desired surface contour, is nonetheless relatively small and therefore its position must be predetermined and fixed relative to the final knuckle position in order to form the proper end turn with reliably consistent repetitiveness. As a result, the knuckle must be rigidly maintained in a fixed position when the universal bending form is used.
A problem thus can arise if the spreading clamps are spread apart equidistantly during the spreading operation by a distance equal to one-half the final spread between the clamps. If the clamps are not initially clamped equidistantly from the knuckle, then moving the clamps equidistantly will create a considerably greater strain upon one end turn coil segment between one clamp and the knuckle than is exerted upon the other end turn coil segment between the knuckle and the other clamp. The result is a significant deformation of the conductors in one of the end turn segments.
It is therefore an object of the present invention to provide a structure which permits the clamps to be moved apart to a selected, finished distance between the clamps, which permits the relative position of the knuckle and the forming surfaces to be fixed and yet automatically applies, without the need for any precalculation, and equal force to both of the end turn segments of the coil on opposite sides of the knuckle between each pair of clamps and its nearby knuckle.
Some prior art machines use two radial arms with a clamp on each arm. The pivot axis of these arms was considered analogous to the center of a stator or rotor so that the distance from this pivot axis to the clamps had to be equal to the radius of the stator or rotor. The structure was impractical and was expensive because of the great size required for the larger stator and rotors.